15 Y F. P. sa\dp:s. 381 



greater part of the time that the animal is lactating, ultimately 

 disappearing when the young animal is capable of leading an 

 independent existence. 



In addition to these changes involving the conversion of tlie 

 ruptured follicle into the corpus luteum, certain changes go on in 

 tlie neighbouring ovarian structures. In a general view of tlie 

 ovary in section, when the corpora lutea are formed it is found 

 that the whole section is occupied by these structures (see fig. 17), 

 whilst the general stroma of the ovar}^ is reduced to a minimum. 

 During the ripening of the follicle and during the process of 

 corpus luteum formation the stroma becomes more and more 

 rarefied and more fibrous, probabl}^ owing to the diverting of the 

 blood supply to the nourishment of the follicle and the corpus 

 luteum. This rarefaction is due to the disappearance of some of 

 the connective tissue cells and the imbibition of fluid by the 

 connective tissues generally. During its progress the larger 

 vessels of the ovary and their branches between the corpora 

 lutea become filled with blood; this congestion of the ovary 

 during corpus luteum formation is a marked feature of the organ. 

 This rarefaction persists whilst the corpora lutea are present in 

 the ovary, and only with their disappearance does the ovarian 

 stroma resume its ordinary condition. 



The theca folliculi is affected in the same way. It undergoes 

 changes in the later stages of corpus luteum formation. Its 

 external part participates in the changes of the ovarian stroma, 

 whilst its inner part (the rudimentar}- theca interna) has the size 

 of its cellular nuclei increased, and is best preserved in the places 

 where it is sending in its connective tissue processes towards the 

 centre of the corpus luteum. 



In addition to the development of the corpora lutea, and the 

 changes in the stroma just described, other processes go on simul- 

 taneously in the ovary. If an ovary be examined at the time of 

 ripening of the follicles or shortly after they burst, it will be 

 found that it is crowded with young ova and follicles in various 

 stages of development (see fig. 2). The smallest and 3'oungest 

 ova are found immediately below the surface, in the intervals 



